In a well drilling process, the rotating drilling stem inevitably comes into contact with the casing or rock well wall and thereby produces friction force, resulting in increased torque, decreased drilling rate, and abrasion of the drilling tool. If the friction force is too high, complex downhole conditions, such as difficulty in tripping operation, caving, or jamming of drilling tool, etc. may occur. Hence, often a lubricant has to be added into the drilling fluid to improve the lubricating property of the system during well drilling, reduce frictional resistance in the drilling process, prevent the occurrence of complex downhole conditions (e.g., jamming of drilling tool), and ensure safe and quick well drilling.
Presently, there are great varieties of lubricants for water-based drilling fluids, and these lubricants are widely applied, while researches on lubricants for oil-based drilling fluids and products of such lubricants are rare, owing to the excellent self-lubricating property of oil-based drilling fluids. However, as the drilling depth and difficulties increase, especially as more and more extra-deep wells, extended reach wells, horizontal wells and cluster wells are drilled, even oil-based drilling fluids can't solve the problem of high torque and severe wear in the drilling process; consequently, downhole accidents, such as caving and jamming of drilling tool, etc. occur frequently.